DESCRIPTION (Adapted From The Applicants Abstract): The neuroimaging study proposed presently differs from many of the extant studies of the neurophysiological effects of HIV/AIDS in several substantive areas. For example, the proposed study will not focus exclusively on thc subset of HIV/AIDS patients with profound dementia in the terminal stages of disease. Secondly, it will also not focus exclusively upon verifying a neurological or neuropsychological staging system which is subjective and has unknown specificity and reliability. Thirdly, the proposed study will not exclude HIV/AIDS patients who are female or possess comorbid psychiatric disorders. The focus of the proposed study will instead be directed toward the quantitative assessment of degrees of impairment in a broader sample of HIV/AIDS patients using objective and reliable neurophysiological tools. For this purpose, we will recruit 120 HIV-1 seropositive and 120 HIV-1 seronegative subjects. All of the subjects will undergo identical procedures which will include structured medical and psychological evaluations. An attempt will be made to match the groups on several neurophysiologically relevant background variables (i.e., depression level, drug use history, gender, and age). The dependent measures will include several quantitative electroencephalographic measures, sensory evoked potential latencies and amplitudes, and topographic analyses of endogenous event-related potentials. Additional dependent measures will include objective and quantitative measures of balance, tremor, and eye movements. The overall goal of the study will be to construct a multivariate model in which one can test the role of various risk factors (e.g., antisocial personality disorder), comorbid disorders (e.g., mood disorder; cocaine, alcohol, or heroin dependence), and markers of disease severity (e.g., CDC clinical stages A, B, or C; viral load, CD4+ count, TNF-alpha) in either mediating, amplifying, or adding to the degree of neurophysiological impairment. In addition, cerebrospinal measures of cytokine and beta-chemokine activity will be gathered for the purpose of examining their correlation with neurophysiological functioning in the subset of HIV/AIDS patients who consent to a lumbar puncture. A secondary study will evaluate the same measures listed above among 45 HIV/AIDS patients before and 3 months after the initiation of a standard antiviral medication regimen as compared to 45 unmedicated HIV/AIDS patients (because of medication intolerance or noncompliance) who are also tested twice. An analysis of change scores across groups will permit a formal test of the effects of antiviral treatment on neurophysiological status.